Gravity measurements



Nov. 12, 1940. e. A. Isms 232L430 GRAVITY MEASUREMENTS Filed Feb. 11, 1958 Patented Nov. 12,1940

UNITED STATES PATENT OFFICE I Y 2,221,480 GRAVITYMEASUREMENTS I Gustaf Adolf I sing; Djursholm, Sweden Application February 11, 1938, Serial In Sweden February 11, l9 7 .3 Claims.

The present invention relates to an apparatus for carrying out gravitymeasurements,said apparatus comprising an astatized pendulum. Astatized .penduluins of various construction,

vertical quartz, rod, which, at its .lowerend, is

secured to the middle 'of a horizontally stretched urements and to facilitate ;the:measuring. work.

The practical importance of relative gravity Incasurements has increased considerablyduring. the

last fewyears, in thatesuch measurements have been introduced for prospecting purposes, it e. for

geophysicalresearches, for. instance insea-rch of.

mineral or oil deposits.

As is well known, the coefiicient of restoring force orcontrol of an astatized pendulum is com posed of a positive or stabilizing component, as a rule of elastic origin, and of anegative or labilizing component which may be due to the weight 1 of the pendulum only. If thepositive component bedesignatecl h and the negative component be i designated 7c the resultant control will evidently behfik, and the moment Q, which at the ipena pendulum which quotient may termed the astatization figure of the pendulum. This figure varies with i the gravitational acceleration. :In fact, the percentage Variation of the control and consequently of the astatization figure is manytimes greater thanthe percentage variation of the gravitational 1 acceleration, thus permittingof a very accurate measurement of '1 the changes of gravity. Ex-. pressed ina formula; If the acceleration g undergoes a. small change Ag, the astatization figure N is consequently subjected to a change AN,wwhich is related to'ng as follows: 3

AN a! the gravity being supposed :to have an: influence only on the labilizing component k of the control.

For a suitableastatization the factor N +1 may be of the order of magnitude of 500 toa 1000.

quartz fibre, the fibre serving as the elastic turne ing axis of the pendulum. Theinvention hasfor its object to increasethe accuracy: of such measi Accordingto the present invention the. determination of therelative magnitude or change of, the astatization figure N is carriedout by bringi ing the pendulum; through a periodic application of a deviating moment thereto, to deflect symmetrically from its vertical positiontowards opposite sides. at constantintervals of time, so that the elastic lag or after-working in the elastic turning axis of the pendulum will have a constant influence on every reading; or recording of the deflectionn The deflecting moment may be produced; for instance by slightly tilting the frame i portion supporting the pendulum at equal time intervals by meansof a. time mechanismfor. ex-. ample a clockwork. The; error ofmeasurement caused by. the elastic lag will thenloecome prace tioallyv the same for all. readings or recordings. Since the measurements are relative, said error of measurement will therefore be substantially eliminated, resulting in a substantiallyincreased accuracy which is of particular importance in measurementsof the accurate nature inview.

The astatization figure N can be. directly obtained from the ratio between the angle of tilt (p of the pendulum supportand the corresponding deflectiono of the astatized pendulum with respect, to its said support the following relation being true for small angular deflections A further increase of accuracy may he obtained by taking photographic records of the pendulum deflections with a certaintime lag in respect to the tiltings offthe support imder control of the same time mechanism used for. effecting the tilting, so that each recording will occur at accua rate ly predetermined intervals of time after the corresponding tilting of the support.

The inventionwill now be described with ref er ence to the drawing attached tothis specification and iormingpart thereof, in which Figure 1 shows a section of an instrument intended to be used for carrying out the methodaccording to the in-.

vention, whereas Figure 2 shows, in another section, the tiltable support for the astatized pen.- dulum. Figures 3 .andfl are diagrammaticviews. of further modifications of the invention.

The pendulum device is enclosed in a doublewalled casing l, 2, the space between the walls. being filled with melting ice or some other medium having a constant temperature. The movable support for the pendulum consists of a block means of the string 1 in the fork shaped holder 6. According to the invention said holder is mounted on the top of the block v3. The pendulum should be comparatively short to obtain a short time of oscillations and at the same time it should be as light as possible so that the air damping will become great. Inserted in the frame right opposite the normal position of equilibrium of the free end of the pendulum is a microscope objective 8, and in line with said objective is arranged an ocular 9. convergent lens system H) inserted at the oppo site side of the frame illuminating light is projectedfrom an outer source of light towards the pendulum point. In front of the ocular 9 a photographic plate or film II is movable in a direction upwards. In the example shown a film is used, said film passing over a wheel l2 which is" rotated a half revolution at constant time intervals under the control of a clockwork 2| operating a spring actuated ratchet wheel 22 so that the film is advanced step by step; The wheel I2 is provided with an eccentric l3 cooperating with one arm of anangle lever M the other arm I of which is connected through a wire I5 with'an upwardly extending arm on a spring actuated angle lever 16 which is pivoted above'the-pen dulum outside of the casing. Pivotally connected its middle position.

Thefblock 3 is balanced in' such a manner that in the absence of the weight the block willtilt slightly towards one side and with the weight hanging on will tilt through the same angletowards the other sidef When the wheel l2 occupies the position shown on the drawing; in which the angle lever I4 is displaced clockwise by the eccentric I3, the rod I'l will occupy its lowermost position, the loose weight l9 then resting on the knife edge 20, causing the block 3 to make a slight deflection towards one side in respect to On the advancing of the wheel l2 one step that is, a half revolution under the influence of the clockwork, the rod I! will be raised lifting the weight l9 off the knife edge, resulting in that the block 3 will now 'tiltthrough an equal angle towards the other side in respect to its middle position. On each turning of the wheel I2 the photographic film will be advanced one step, and after the lapse of a definite time interval a momentary exposure of the film for instance, by closing the electric circuit for the source of light will be effected by means or the clockwork.

In the shown example the ocular 9 is assumed to be slightly movable parallelly with the deflection of the pendulum point, i. e. at right'angles to the plane of the paper in Figure l, and to be connected withfthe stepping mechanism in such a manner that upon each deflection of Through a l4 so that the ocular will be subjected to a re-' ciprocating movement in synchronism with the tilting movement of the support 3. It is hereby rendered possible to use a rather narrow film.

The same object can be attained by providing two fixed oculars, Figure 4, located at opposite sides of the optical axis of the objective 8.

The described embodiment represents merely an example of the invention. The arrangement for effecting the periodical tilting of the pendulum support can be devised in different ways.

The arrangement can also be such that the film ismoved continuously instead of step by stepand independently of the mechanism for the periodical changes of tilting in which case the ec- I centric I3 is alone driven over the ratchet wheel 22 while the wheel 12 is driven directly by the same or by another clockwork, If desired a stationary film or plate may be used and the ocular 9 may instead be operatively'connected with the clockwork by means of a suitable transmission so as to be displaced perpendicularly to the defiections of the pendulum.

I claim:

1. An arrangement for carrying out gravity measurements comprising in combination a tiltsaid support, a time mechanism, an'automatic operating mechanism adapted to tiltsaid support periodically under the control of said time mechanism so as to cause the pendulum to swing over through its vertical position, and means for-determining the deflections of said pendulm.

2. An arrangement for carrying out gravity measurements comprising in combination a tiltable support, an astatized pendulum mounted onsaid support, a time mechanism, an automatic operating mechanism adapted to tilt said support periodically under the control of said time mechanism so as to cause the pendulum to swingover through its vertical position, means for projecting an image of an indicating point of the pendulum on a light sensitive recording surface and means operating in synchronism with the tilting of said support to bring about a stepwise relative displacement between said light sensitive surface and said image perpendicular to the displacement caused by the pendulum deflection.

3. An arrangement according to claim 2, including means effecting also a lateral displacement of the projected image opposite to its dis placement caused by the pendulum deflection, thus permitting the recording of the symmetrical deflections to be-efiected within a comparatively narrow zone or strip of the light sensitive surface.

GUSTAF ADOLE ISING.

able support, an astatized pendulumnlounted on 

